Certain Sugars Stimulate Appetite, Study Finds

Different kinds of sugar affect the brain differently, specifically the feeling of satiety, according to a new Yale University study.

According to the researchers, "increases in fructose consumption have paralleled the increasing prevalence of obesity, and high-fructose diets are thought to promote weight gain and insulin resistance."

Consumption of fructose, which includes refined table sugar (technically sucrose, a combination of fructose and glucose) and high-fructose corn syrup, led to smaller increases in circulating satiety hormones compared to glucose ingestion, the researchers found. Glucose is found in fruits and vegetables and in starchy foods like bread, pasta and rice. In fact, the study found that administration of fructose actually provokes feeding in rodents, while glucose administration promotes satiety.

The experiment involved 20 healthy adult volunteers who drank either a cherry-flavored fructose or glucose drink in a blind, random study, MedPage Today reports. The subjects were then given brain MRIs. Those who had consumed the glucose drink had significant reductions in cerebral blood flow to the hypothalamus, a region of the brain associated with appetite and reward. Those who drank the fructose concoction, on the other hand, saw a slight increase in activity in this area. Robert Sherwin, MD, of Yale University, and his colleagues reported the results in the January 2 issue of the Journal of the American Medical Assn.

Glucose also reduced activation in the insula and striatum, other brain regions that regulate appetite, motivation, and reward processing, while fructose did not, the researchers wrote.

Participants rated their feelings of hunger and satiety before and after the scan, and the researchers took blood to assess circulating hormone levels. The differences in brain effects between glucose and fructose also appeared to coordinate with ratings of hunger, since there was a significant difference from baseline in terms of fullness and satiety when participants drank glucose, but not fructose.

And the blood tests showed that fructose only weakly stimulates secretion of insulin, a hormone that can increase satiety, and attenuates levels of the satiety hormone glucagon-like peptide-1 (GLP-1) -- which means it could possibly increase food-seeking behavior and intake.

In an accompanying editorial, Jonathan Purnell, MD, and Damien Fair, PhD, of Oregon Health & Science University, said the findings "support the conceptual framework that when the human brain is exposed to fructose, neurobiological pathways involved in appetite regulation are modulated, thereby promoting increased food intake."

Purnell and Fair noted that while some researchers and clinicians warn that the total amount of calories is more important than the type of food when it comes to losing weight, the "reality ... is that hunger and fullness are major determinants of how much humans eat, just as thirst determines how much humans drink. These sensations cannot simply be willed away or ignored."

The upshot: High-fructose corn syrup is bad, mmmkay? But you already knew that.